The present invention relates to a latch device which is used when coupling and decoupling (engaging and disengaging) a movable body on a main body, particularly a push-push type (this also may be called a push lock-push open type or alternating type) latch device, and an opening and closing apparatus using the same.
A push-push type latch device has a cam member and a pin member which couples and decouples with that cam member, respectively, provided in correspondence on the movable body and the main body, locks the movable body in a first position of the main body via the coupling of the pin member on the cam member, and releases said coupling by pushing from that first position and then releasing that pushing force to enable switching to a second position, and it is excellent in the point that locking and release can be accomplished by push operation of the movable body. Device structures are largely divided into swing type exemplified in FIGS. 12(a), 12(b), and heart cam type exemplified in FIGS. 13(a), 13(b).
The latch device (lock device) in FIGS. 12(a), 12(b) is one which is given in Japanese Unexamined Patent Application Publication No. 2002-303070, and FIG. 12(a) shows the locked state, and FIG. 12(b) shows the unlocking process. In this example, the movable body 51 is a drawer, or the like, and it is pushed in toward the C direction being the stored side with respect to the case 50 in opposition to the impelling force of an impelling means not illustrated, and conversely is impelled to move toward the O direction being the side for use. The latch device 52 comprises a cam member 53 which is provided on the case 50, an impelling spring 55 which impels that cam member 53, and a pin member 54 which is provided on the movable body 51, and it locks the movable body 51 in the stored position by push operation, and releases that locking by the next push operation.
Here, the cam member 53 comprises a front piece 56 and a rear piece 58 which is spaced by a vertical slit 57. The front piece 56 has a sloping cam face 56a which forms a front end edge, a locking cam groove 56b which is provided on a part of the rear end edge, and a straight sloping cam groove 56c for releasing which extends in the front-back direction. The rear piece 58 has a shaft attachment hole, a projection 58a which projects out from the front end edge toward the cam groove 56b, and a contact projection 58b which is placed projecting on the rear edge part. Also, the cam member 53 is pivotally supported on the side of the case 50 to be capable of rotating via a shaft S. The impelling spring 55 has one end fixed to the cam member 53 and the other end fixed to a stopper 59 which is placed to project on the side of the case 50, and in that state it is impelled to rotate in the clockwise direction by the impelling means 55 until the contact projection 58b strikes the corresponding end of the stopper 59.
The operating characteristic is that when pushing the movable body 51 into the case 50 by push operation, the pin member 54 strikes the sloping cam face 56a, and then enters as far as the cam groove 56b while making the cam member 53 rotate counterclockwise in opposition to the impelling spring 55 with the shaft S as fulcrum. When the pushing force is released, the cam member 53 rotates clockwise by the impelling force, and the pin member 54 is coupled in the inside angle part of the cam groove 56b. The movable body 51 is locked in the stored position by that coupling. When drawing the movable body 51 from the case 50, in case the movable body 51 is pushed, the pin member 54 moves from the cam groove 56b to the straight sloping cam groove 56c as in FIG. 12(b) with accompanying clockwise rotation of the cam member 53. When the push operation is released, the pin member 54 moves following the straight sloping cam groove 56c, and at the same time, the movable body 51 is moved toward the projecting direction by the impelling force. The symbol 60 is an inertial stopper which is guided by a guide 61 and is pushed forward by a spring 62. When the movable body 51 receives inertial force the same as push operation in the stored position, the inertial stopper 60 progresses backward in opposition to the spring 62, and as in FIG. 12(a) it approaches the corresponding side part of the cam member 53 whereby it disables rotation of the cam member 53 toward the unlocking direction.
The latch device (latch means) in FIGS. 13(a), 13(b) is one which is disclosed in Patent Document 1 (Japanese Patent No. 3671824), and FIG. 13(a) shows the entirety of the latch device in the cover closed state, and FIG. 13(b) shows the essential parts of the cam member. In this example, the cover 2 is rotated toward the closed direction on the box 1 in opposition to the impelling force of an impelling means and is locked in the closed direction via the latch device 4. The latch device 4 has a heart-shaped cam 6c which is provided on the side of the box 1, and a pin member (movable pin) 54 which is provided on the side of the cover 2, and it is similar to the spring type in the point that the cover 2 is locked in the closed position by push operation, and that locking is released by the next push operation.
In the latch device as above, when an excessive load in an improper direction (for example, excessive load due to forcefully pushing the hinge side of the cover or forcefully prying open the open end side of the cover) is received with the cam member and the pin member coupled, that is, in the cover closed state, the tip of the pin member 54 which is in the coupled position is pushed up from the cam groove and comes off from the cam, and the cover easily becomes left open or left closed. Also, the cam part may become abraded and the coupling position with the pin member may shift and the feeling of operation may become worse, moreover when it is unlocked forcefully, it may cause deformation, breakage or falling off of the pin member, as well as an uncomfortable noise.
Therefore, in the latch device in Patent Document 1, a countermeasure as follows is adopted. That is, in this structure, it is constituted by a heart-shaped cam 6c having a first cam groove 6a, a second cam groove 6b, and a locking recessed part 6d, and a pin member 7 of which the tip part is coupled in the locking recessed part 6d while sliding in said first and second cam grooves. In the vicinity of the locking recessed part 6d of the heart-shaped cam 6c, there is formed a beveled part 6i, or the like, where the tip of the pin member 7 springs out to the side of the first cam groove 6a or the second cam groove 6b when forceful pushing-up force acts on the tip part of the pin member 7 locked in the locking recessed part 6d. 
With the above countermeasure of the past, although the beveled part or a sloping face is formed in the vicinity of the locking recessed part on the cam side and it is made as a structure in which the pin member easily comes out from the locking recessed part to the side of the first cam groove or the second cam groove via the beveled part or sloping face, it is still not satisfactory in terms of aspects as followings. That is, in the countermeasure of the past, the coupling force between the pin member and the locking recessed part, that is, the locking force on the cover, becomes weak and tends to become irregular, and the locking ability becomes worse due to that. Moreover, through continued use, the position of the locking part for locking with the pin member shifts and the locking position of the cover also tends to shift, and the quality cannot be maintained.
Therefore, the purpose of the present invention is to improve the quality and reliability in a swing type or heart cam type latch device, by making it such that the locking part for locking with the pin member is moved to be capable of returning inside the cam member when excessive load in the improper direction is received, so that it does not become abraded or cause a breakage as noted above, and moreover the locking force on the movable body can be kept constant whereby the occurrence of malfunction is suppressed.
Further objects and advantages of the invention will be apparent from the following description of the invention.